Periodontal disease is characterized by morphological changes in collagen fibers of the periodontium. Detailed structural studies at the molecular level of human gingival collagen from normal and diseased tissues are proposed. The biochemical data obtained will be correlated with the histopathological observations and clinical manifestation of the disease. Such correlation will provide valuable information on the role of the intercellular macromolecules in periodontal disease. Limited proteolytic and cyanogen bromide digestion of the insoluble collagen are used to characterize the bulk of the tissue collagen. Collagen biosynthesis by gingival tissue will be studied in each case (normal and diseased tissues) to examine the effect of disease involvement of gene expression. The nature and structure of collagen in human gingiva may serve as a useful parameter to assess the process of periodontal disease.